It is well known that in a video tape cartridge, there is provided a spring plate of stainless steel fixed to a top plate of the top section of the cartridge with each of the free ends of the spring plate extending to above the corresponding top end of the axis of the tape reel to suppress undesired vertical displacement of the tape reels.
U.S. Pat. No. 3,934,839 discloses one example of a magnetic recording tape cartridge having such a spring plate as mentioned above. In this magnetic recording tape cartridge, the spring plate is fixed onto the inside surface of a top section of a magnetic recording tape cartridge without any partition wall member surrounding the center portion of the spring plate. The spring plate is fixed onto the top section in such a manner that one or more perforations defined in the center portion of the spring plate are inserted in corresponding projections formed on the inside surface of the top section. In turn, the projections are caulked by a thermal deformation using a suitable die with ultrasonic welding. However, when the projection is caulked, some part of the projection expands from the gap between the die and the surface of the spring plate to form a thin plate-like portion. Such a thin plate-like portion tends to be separated from the projection as one or more pieces of fragments due to undesirable force caused by a vibration of the cartridge while the magnetic recording tape cartridge is used. If the separated fragment is undesirably fitted with a magnetic recording tape, drop out of the recorded signals and/or noise may occur when the magnetic recording tape is reproduced.
Another disadvantage being inherent in the prior art magnetic recording tape cartridge is that in assembling the spring plate onto the top section, since relative position between the perforations of the spring plate and the projections formed on the top section is not easily adjusted, it takes time to engage the perforations of the spring plate with the corresponding projections on the top section.